The purpose of an HVAC system is more than just warming or cooling a space. Instead, it serves to improve indoor air quality and provide comfort for everyone inside a building. While there are several different types of HVAC systems, they all begin with the same essentials.First, there is a source of fresh air intake from the outside or from within the home. This process is called ventilation, and it happens in two different ways. Natural ventilation is present in most homes and refers to the way air typically moves in and out through windows, doors, vents, and other openings. This exchange of air is necessary to replenish oxygen, and to remove odours, carbon dioxide, unpleasant odours, and excessive moisture. Mechanical ventilation uses a mechanical system to move air in and out. Once the air is brought in, it is drawn into an air handling unit where the work begins. Here, air is drawn through filters to remove dirt, dust, allergens, and other particles. Next up is comfort. Air is either sent to be heated or sent to be cooled and have excess humidity removed. Once the air is clean, fresh, and at a comfortable temperature, it is directed into the home. For central systems, this means moving through a network of ducts and registers to different rooms. For other systems, this usually means being directed right into the space.